Evidence for a hot dust-free inner disk around 51 Oph*

We report on the observation of CO bandhead emission around <ASTROBJ>51 Oph</ASTROBJ> (Delta v=2). A high resolving power (R≃10 000) spectrum was obtained with the infrared spectrometer ISAAC mounted on VLT-ANTU. Modeling of the profile suggests that the hot (T_gas= 2000-4000 K) and dense (n_H>10¹⁰ cm^-3) molecular material as probed by the CO bandhead is located in the inner AU of a Keplerian disk viewed almost edge-on. Combined with the observation of cooler gas (T_gas= 500-900 K) by ISO-SWS and the lack of cold material, our data suggest that the disk around <ASTROBJ>51 Oph</ASTROBJ> is essentially warm and small. We demonstrate the presence of a dust-free inner disk that extents from the inner truncation radius until the dust sublimation radius. The disk around <ASTROBJ>51 Oph</ASTROBJ> may be in a rare transition state toward a small debris disk object.